WebGPU shader reportedly freezes MacOS UI requiring forced restart across browsers

A WebGPU compute shader with a trivial infinite loop can lock up the GPU on MacOS, causing the WindowServer process to become unresponsive. The shader copies data in an endless loop while a dependent vertex shader waits for access to the same buffer. This contention propagates to the system UI, freezing the desktop until the watchdog triggers a kernel panic or the user forces a restart.

The vulnerability is specific to MacOS and reproduces across all major browsers supporting WebGPU. Other operating systems handle the same shader by freezing only the affected tab, allowing recovery without a system restart. This suggests MacOS lacks effective preemption for GPU tasks originating from untrusted web content, a gap not present in other platforms.

Apple’s M-series architecture may contribute to the issue, as GPU preemption logic resides in the ASC coprocessor firmware rather than the OS kernel. This separation complicates real-time intervention when a shader becomes unresponsive. Previous mitigations for WebGL vulnerabilities relied on input validation, but detecting infinite loops is fundamentally limited by the halting problem.

The disclosure timeline indicates Apple initially acknowledged the issue but later shifted its response. No fix has been released, leaving MacOS users exposed to potential denial-of-service attacks via malicious websites. Engineers should monitor for updates and consider browser-level mitigations or WebGPU restrictions for critical systems until a patch is available.